There are a standard that extends a channel width to 40, 80 or 160 MHz, based on a reference channel of 20 MHz width. In this standard, the following bandwidth operation methods are defined: a method called a dynamic method which returns a response in a maximum channel width determined to have no interference and containing the reference channel; and a method called a static method, which does not return a response (i.e., cannot acquire any available channel) if at least one of channels used for transmitting reception frames has interference. Terminals in conformity with this standard mandatorily support at least a bandwidth up to 80 MHz.
Meanwhile, there is a system that is called OFDMA (Orthogonal Frequency Division Multiple Access) or Multi-user Multi-Channel (MU-MC) system, and simultaneously performs transmission destined for multiple terminals in multiple channels or reception from multiple terminals. In the MU-MC system, an MU-MC compliant terminal is expected to be capable of detecting CCA (Clear Channel Assessment) in an individual channel basis and to perform the dynamic operation in response to interference detection, in order to increase throughput by efficiently obtaining a free channel. Also in a case where OFDMA that performs allocation to terminals on a subcarrier basis (Resource Unit; RU) is applied to IEEE 802.11 wireless LAN, it is expected to detect CCA in a unit of existing reference channel width, such as of 20 MHz width, and to perform the dynamic operation in response to interference detection. Furthermore, efficiency of channel use is improved by not imposing the limitation on channel usage with a channel width based on the reference channel as in the afore-mentioned standard, allowing transmission on an individual channel basis, and performing transmission via a channel without interference.
However, in a case of using a channel with at least 80 MHz width and accommodating terminals that support the afore-mentioned standard as legacy terminals, there is a possibility that use of a channel width of 80 MHz or a channel width of 160 MHz by the legacy terminals, particularly, terminals supporting the static method, reduces the efficiency of channel use over the entire system.
Thus, to maintain the efficiency of channel use over the entire system in a high level, it would be better to limit at least use of wide bands by legacy terminals that support the static method. However, legacy terminals do not have means for explicitly notifying another terminal which method the terminals operate in between the dynamic and static methods. Consequently, it is required to assume at least a presence of a legacy terminal that operates according to the static method.